The present invention is generally directed to the centrifugal treatment of liquids. More specifically, the present invention is directed to the separation of components from blood or plasma.
Whole blood can be separated or fractionated into its various individual components by utilizing a centrifugal blood separator. In an intervivos blood processing apparatus, whole blood can be taken from a live donor, passed through the apparatus, and then returned to the donor. During the passage of the blood through the apparatus, the blood can be separated or fractionated into its component parts, e.g., plasma, red blood cells, platelets, and other components. Some portion of these fractions can be selectively retained within a suitable storage member and other portions of the fractions can be returned to the donor.
Various types of apparatus are utilized for the intervivos processing of blood. One type of apparatus is described in U.S. Pat. Nos. 3,489,145 and 3,655,123. The apparatus utilizes a centrifugal separator element in the form of a rotatable driven bowl-shaped outer shell within which a cylindrically-shaped center or filter piece is suspended to form a narrow sleeve-shaped separation chamber of very precise dimensions. Fluid connections are established within the chamber by use of a rotating seal, the chamber having an axially-aligned inlet port at one end for admitting whole blood, and a trio of collection ports at the other end for removing red blood cells, white blood cells, and plasma components separated during centrifugation.
Systems for carrying out intervivos blood processing typically include a separation chamber within which whole blood from a donor is subjected to a centrifugal force field. Because of the differences in density, the blood components are congregated in zones at different radial distances from the center rotation of the separation chamber. Collection ports in the chamber remove the components from these zones for storage or recirculation.
In separating the components, it is necessary for the separated components to be consistently of high purity. If the blood components are subjected to intermixing, it is necessary to discard at least a portion of the separated components providing an effective lower yield for the system.
U.S. Pat. No. 4,146,172 discloses, in an embodiment, an intervivos blood processing system including processing chambers for centrifugally separating red blood cells, and platelet components from whole blood. An example of such a system is the CS-3000.RTM. sold by Baxter Healthcare Corp., Deerfield, Ill.
The system includes a thin processing chamber having first and second closely spaced side walls defining an interior chamber including at least one collection region, outlet means for withdrawing fluid from the collection region of the chamber, and means including inlet means and an additional outlet means defining a flow path for delivering blood to be processed to the chamber. Means including a rotatably driven carriage are provided for rotating the chamber with the chamber mounted generally perpendicular to a radius of the rotor whereby the red blood cell component is caused to collect in the collection region of the chamber.
Although the described system functions satisfactorily for separating red blood cells and platelets from whole blood, for certain applications such as, separating mononuclear cells, this system may not function optimally. When so used, the collection chamber tends to retain platelets leading to a mononuclear cell product that is contaminated with platelets. Typically, at least approximately 50% of the platelets are retained within the collection chamber. It has been found that a retention of over one-third of the platelets in the mononuclear cell product does not provide a satisfactory product for certain applications.
The retention of platelets within the collection chamber not only represents a disadvantage because mononuclear cells and the platelets are intermixed but also can have deleterious effects on the donor. Donor thrombocytopenia is associated with multiple frequent donations of mononuclear cells due to a loss of platelets.
Known collection chambers typically are also too large for a mononuclear cell collection process. For example, one commercially utilized chamber has a volume of approximately 200 cc. This is generally considered too large for the collection of mononuclear cells, i.e., for a stem cell procedure. With such a large volume chamber, additional volume reduction is required and/or additional processing such as a density separation using Ficol-Hypaque to remove the platelets is necessary.